1. Field of the Invention
The present invention is generally concerned with filters used to clean a liquid circulating in a network under pressure and likely to entrain debris, detritus or foreign bodies.
It is more particularly directed to treatment of industrial process water which may contain man-made debris or detritus and/or vegetable debris or detritus, such as algae, for example, or animals such as mussels, shellfish or fish liable to proliferate on the downstream side unless previously separated out.
More specifically still, the invention concerns steam condensers.
2. Description of the Prior Art
Filters used to clean industrial process water usually comprise a filter body to which is connected a screen, that is to say a filter element that may comprise a screen of perforated sheet metal or filter fabric, or a screen formed by an array of parallel blades or filaments carried by transverse support bars, the screen being designed to be inserted into the flow to be treated.
In the specific case of self-cleaning filters means are provided for systematically evacuating debris, detritus and foreign bodies held back by the screen.
Thus in known implementations, which have the considerable advantage of comprising no moving parts, such evacuation results from design features which cause the incoming flow to sweep across the screen.
For example, in a first type of implementation of such self-cleaning filters without moving parts the arrangement is such that the speed vector of the incoming flow is oblique to the surface of the screen and thus has not only a component perpendicular to the latter, necessary to have the flow pass through the screen, but also a tangential component; by virtue of this latter component any debris, detritus and foreign bodies held back by the screen are systematically and continuously entrained towards a collecion space provided for this purpose.
In this first type of implementation of self-cleaning filters using no moving parts the filter body is in practise disposed around the screen in the manner of a spiral staircase, the flow to be filtered entering the filter body tangentially and the treated flow leaving it axially.
Although giving satisfaction, the corresponding implementations are for the most part somewhat bulky and since they change the orientation of the flow to be treated, which also and inevitably results in head losses on the downstream side, they can be difficult to install, especially in existing installations, and so are not suitable for all applications.
The existing installation must have either sections of conduit at right angles to each other or sufficient space for such sections of conduit to be installed.
In a second type of implementation of self-cleaning filters using no moving parts the filter body is adapted to be inserted in the flow direction in the conduit carrying the fluid to be treated, the corresponding screen then having a generally conical filter wall which has its larger diameter end, the upstream end, at least partially fitted within the filter body, there being in the filter body and around the larger diameter end of the screen a transverse volute-form collection space to which is connected an offtake conduit for evacuating debris, detritus and other foreign bodies held back by the screen.
However, in this second type of self-cleaning filter with no moving parts the screen is in practise cleaned only during periodic purges, the feed water for such purging then causing the incoming flow to rotate to bring about the necessary cleaning action; these periodic purges, which are diverted to the drainage system, mobilize quantities of water prejudicial to a regular feed to the downstream installation, all the more so in that all of the surface of the screen has to be cleaned simultaneously.
In such implementations it is currently necessary, to ensure an acceptable ratio between the filter surface area of the screen and the cross-section of the conduit into which it is inserted, for the length or height of the screen along the axis of the conduit to be very much greater than, in practice, twice the diameter of the conduit; once again this makes the possibility of installing such filters somewhat random, especially in existing installations, where there are rarely sufficient lengths of conduit between two bends.
In the specific case of a steam condenser the use of this second type of self-cleaning filter using no moving parts can also cause difficulties, especially where the filters have to be installed in the immediate vicinity of the inlet water box of the steam condenser.
It is then necessary to have, between the tube that a water box usually incorporates for connecting it to the conduit which serves it, on the one hand, and the conduit is itself, on the other hand, sufficient space for inserting the corresponding filter body.
A general object of the present invention is an arrangement which, for a self-cleaning filter without moving parts adapted to be inserted in the flow direction into a conduit, advantageously makes it possible to minimize the overall length of the filter along the axis of the conduit whilst providing an acceptable ratio between the filter surface area provided and the cross-section of the conduit, and whilst also procuring at all points on the screen an angle of incidence relative to its surface of the speed vector of the flow to be treated adapted to procure systematic entrainment towards a collection space of debris, detritus or foreign bodies held back by the screen.